Motor control



Dec. 1, 1931. 1.. c. HARDESTY 1,834,777

' MOTOR CONTROL Filed Aug. 5, 1927 Patented De c. 1, 1931 S ATENT;omcs

1- nr nwnnnyn c. HARDi'flSTY, orscorIA, new Yank, ASSIGNOR TQ GENERAL nnno'rmc I T comrnnmn' CORPORATION OF NEW YORK 1 i moroa'conrrnor.

Application M; au us taiszm se ia in. 210,978.

I My invention relates to improvements motor control, and n particular to unprovements in systems of motor control whereby the extent of the independent operation'of one n 1o tor driven element maybe limited' with reference to another element which is independently operatedby another motor,

A particular application of the invention is found in electric drives for bucket'hoists.

' Insuch drives, it is customary'to provide two motors which may be independently operated, One of these motors is connected through a cable to the frame ofthebucket be retained in the bucket; raised by both motors being energized to op-, fferate as motors and'applya hoisting effect; When the bucket has been moved to theFdesired position, the load of material is dumped andis' commonly called the shell motor or holding line motor. This motor is providedfor raising and for governingthe low- ,7 ering of theloucket. The other motor iscon'f nected, through a cable to the opening and closing mechanism ofthe bucket. This Isecond motor is ordinarily calledfthe closing line motor. In general routine work, the

closing line motor closes the jaws jor the I bucket when the bucket has been lowered to i the material to be raised.' ,The jawsof'the bucket close and cause a load of rnaterial to The bucket is then by reversing theclosing line motor while the bucket is held in position, thereby permitting the jaws of the bucket to open. The empty bucket is then lowered with the jaws open and the above described operation is, then. re-

peated;

If one motor is operated so as to operate its associated drum faster than the other motor is operated so as to operate itsassociatedjdrum, or if one motor is stoppedand the other is operated, under certain conditions, an excessive amount ,of cableis likely,

to be unwound from the drunli that is being operated. V Ifthe holdingline motor is not being operated and theclosing motor is operated in the lowering direction so asto un-,

windicable from the closing line, drum andv eflectthe opening ofthejjaws ofthe bucket,

if the closingfline motorfis operatedfafter the jaws of the bucket are opened, an excessive amount of. cable is'unw'oun'd from the I closing line drumf the closing line motor is operated so asto wfind upcable on the 'closing line drum and close the jawsof the bucket,

when the bucket jaws are closed, if the hold; ing line motor is operatedso as to unwind cable from the holding line drum while'the bucket isbeing held by the closing line, an excessive amo'untoi'- cable will be unwound from, the holding line and the slack inthis cable is undesirable. i

Anobject of the invention is to prevent the li'tormation of an excessive amount of slack form which I now regard as the preferred form thereof, I provide a motor control including as a part thereof, I a limit switch mechanism which has cooperating parts each of which is movable in response to the rotation of its respective associated drum. Thus,

whenthefphase angle displacement of "one.

I drawing, in which I have illustrated in verysimple diagrammatic form, a motor control in either the closing line or the holding: line. in carrying my invention into effect in the;

for a grab bucket hoist having a limit switch I incorporated in the control ifor the purpose specified. Thebucket l0 is indicated as of the grcb or"shell type- ;'Ihe"1 jawsof this. bucket areopened andclosed under the con trol of the closing line 11, which has one end thereof secured 'to the closing line drum 12.

This drum is operated by the electric motor 13 which is indicated as of th-e direct current shunt wound type. I would have lt'underother: types of motors'maybe employed'for the operation of the drums and such other types of motors may bealso 'controlledl'in accordance with'the features of the invention,

as will be understoodfiom the following explanation' Themotor 13 is arranged to be connected to the source of supply 14 under the stoodthatthe invention is not necessarily limited to this particular type or motor, since control of the directional contactors 15 and 16 which are governed by the manually operated reversing controller 17. The contactor 15 is provided for effecting the energization of the motor 13 for closing the jaws of the bucket 10and for raising thisbncket and the contactor '16 is provided for efiecting the energization of motor 13 to open the jaws of 'thebucket and govern the lowering'of the bucket. p

The bucket 10 is raised and lowered by means of the holding line 18 which h'us one end thereof connected to the bucket and the other end thereof cemleeted to the holding line drum 19. The drum 19 is operated by means oithe motor 20,'which'is alsoindicated as of the direct current shunt'wound type, although the invention is'not necessari- 1y limited'to thistype of motor, as wasexplalned previously. The motor 20 is con- 4 nected to the direct current source of supply 14 under the control ofthe directional'conta'ctors"21 and'22 which are governed by means of the manually operated master switch 23. The directionalcontactor2l is provided for eflecting'the energizatioirof motor 20 to hoist the bucket 10'and the directional contactor 22 is provided'for effecting' the connection of motor20'to source '14:

"for 'o'vernin the'lowerin of bucket 10.

. .D b D I'have merely shown a simplified control for the motors 13 and 20, as previously explained. HoweverfI would have it understood "that'these bucket hoist controls'are sometimes quite complicated and incorporate features such'as dyn'an ic braking of the motors to govern'the lowering of the bucket and various other features.

I'have not shown such features, 'sincethey are not of theessence of the'present'invention audit is believe'd' that th'e'in'vention will bebetterun tieular case require.

derstood by reason of the elimination of those features and from the'further fact that those skilled inthe artwillreadily supply such furtherieatures as thenecessities of the par- In order to prevent either motor from operating its associated drum insuch'a manner and to such an extent that the formation of slack in the'cable associated with the other "drum either occurs or is likely to occur, I have provided the differential limit switch 2 1.

This switch is provided with two cooperating parts; each of which 1s connected to an associated drum so as to be operated 1n synchronism therewith. Oneof these parts'comprises the'conducting rings 25,- 2G and 2'7, toigcther with the brush holder 28 and the brushes 29, 30 and 31. This limit switch part is operated in accordance with t-he'operation of the drum 19 by being connected to said drum in any suitable manneig'as for instance "bymeans oi the belt 32, which'is shown. The

other controller part CUIDPIlSBS'thG drum con troller having the conducting ring 33, and

ment with the segment 34. brought aboutwhen the jaws of'the bucket "are fully closed.

indicated in thedrawing, the operation of my invention is as follows: In order to close thejjaws of the bucket 10 and efiect the raising of the bucket, the controller 1'? will be thrown toward the left so as to efieet the .energization of the directional contactor 15.

This will cause themotor 13 tobe energized in such a directionthatthe drum -12will be rotatedtowind upthe closing line 11. As the drum12 is'rotated, thepart of the limit switch mechanism 24: which includes {the ring 33, and segments 34: and35 will be rotated in such 'adirection that after a predetermined extent of movement of the drum 12, the brush'30 willbe'moved'out'of engage- 'This will be It will be observed that the energrzlng'clrcuitfor the winding of contactor 15 is from the lower conductor of source l i, the rightehand contacts of master SW1tCl117,'W1I1(liI1g of contactor '15, conducting'ring26, brush 30, conducting segment 34: and ring 33, ring 27, to the upper supply conductor. Asthe motor-13 operates to close the aws of the bucketyassuming that-the motor 20 is not'being operated, the segment 34 of the limit switch arrangement will be moved so" that the brush 30' is out of engage mentthereWith. This will interrupt the energlzlngcircuitfor the contactor 15 and the motor 13 will be stopped.

."It 'will also be observed that the lowering 'contactor 22 for the motor 20 cannot be energized because of the fact that the' circuit for the 'win-dingof'contactor 22'is traced through thesegment 34i'and brush'30 of the limit switch '24. As a consequence; the motor 13 is stopped'when the' jaws of the bucket are fi'ully closed and the bucket jaws will be held in'this closed position byany suitable means,

such as the common and well known'series electro magnet'brake which when deener- "gized-applies africtional braking e'fiect'to hold adriven device. I that the eontactor 22 cannot be ener g'ized, theoperation'of the-motor 20 in the lowering direction is prevented. This is desirable,

Because oi the fact since if it werepossibleto operate the motor 20 in the lowerlng direction, the holdingline would beun-woun'd from the drum 19 to such anextcnt that there would be an undesirable slack in this line. The motor 20 may nevertheless -be operated in the hoisting direction by throwing themaster switch'23 to the left,

thereby energizing the directional contactor 1- of contactor 21, conducting ring 25 of limit, switch 24, brush 3l, segment 35, ring .33,

' wound 211mm the lower conductor of source 1 1, right-hand contacts ofmaster switch 23, coil brush 29, and ring 27 of; the limit switch to the upper conductor of source 14. V

'It is desirable that both motors 13 and be operated when the bucket is to be r ised. Both motors are thusefl-ective to provide a hoisting action and further the jaws of the bucket are prevented from openin In order to insure this, the limit switch 24 provides a control whereby if the motor 20 is operated to such an extent wound up a predetermined length of cable while the drum 12' remains stationary, the i contactor 21 will be automatically opened. Thus, when the drum 19 is operated to wind cable thereon, the brush holder 28 and the associated brushes 29, 30 and 31 will be rotated synchronously with the drum 19. After a predetermined extent of movement, the" engagement with the brush 31- will break segment 35 and thereby interrupt the energizing circuit for contactor 21, thus stopping the motor 20 from further operation in the However, it when the;

hoisting direction. jaws of the bucket .are closed, both motors 13 and 20 are simultaneously operated, the phase angular displacement between the two relatively movable cooperating parts of the limit switch, 2 1 will be such that the bucket be raised and lowered at the will of the operator.

.r-issume that and it is desired to open the same. ter switch 17 will be thrown that a circuit is made from the lower conductor oi sou be 1 1, coil of contactor 16, conducting ring 25, brush 31, segment 35, conducting ring 33, brush 29, conducting ring 2'? to the upper conductor of the source 1 1. This will efiect the closing of contactor 16 and the motor 13 will be energized so asto unwind the cable troin'the drum 12. This will eii'ect the opening of the jaws of the bucket so that the material in the bucket may be spilled therefrom. During this unloading operation, it has been assumed that the bucket The masassumed that the drum leased friction brakes are commonly provid plate the provision or such holding devices for both the drums 12 and 19. I When the predetermined length 'ofcable has been ununwinding operation of the winding of contactor16 is opened.

ly the in the drawm that the drum 19 has.

the bucket has been raised to the right so -cuit for the directional cont-actor 21 is also same time that the circuit for This willprevent the formation of slack inthe holding cable 18, since the motor 20 cannot be energized'so as toeltect the lowering of the opened at the bucket until the cooperating parts of the limit switch 2 1 have been returned to practical- It willbe observed from the foregoing that control over the ordinary manipulation of the;

manner that slack'cable will be formed in phase angle relation which is indicated V 'while a control in accordance with my in- .vention gives the operator of the hoist full 2 either the holding line or the closing line the functioningot thelimit switch 24 will "automatically prevent this being done. It will also be observed that the control is such that the limit switch does not shut down the equipment,bu t merely necessitates that the operator operate the erpiipmentv in such av manner that he will not form slackcable in either one of the cables. Those familiar with bucket hoists, for example, willreadily, appreciatethe advantages of such control.

\Vhat I claim as new and desire to secure by Letters Patent of the United States is 1. In a motor control, two separately ope'rafble,motors,separately operable elements connected to be operated by said motors, and; means automatically operated'in dependence on the occurrence or" a predetermined phase difference in said elements for insuring limited independent operation of both of said motors in both directions of rotation. e r

2.111 a motor control, two separately op erable motors, separately operable elements connected to be operated by said motors, independently operable starting'and reversing and electrical connections between said controlling means including limit switch mechanism having cooperating parts connected to the respective elements to have relative movement in response to relative movement of the elements to eliect the automatic stopping of the motor being operated and the prevention of the starting of the other of said'motors to increase the phase angle 'fdisplacement of ithe elements. 7 ed for thus holding the drum and I contem-c V 3. In a bucket hoist, a holding drum and cable 7 connected thereto for governing the hoisting and the loweringof-the bucket, an I independently operable closing drum'and a from drum 12, the segment 35will break engagement with brush 31 andstop the drum n 12. It will i also be, observed that when the jaws oii'the" bucket are thus opened, the motor 20 cannot be energized so asto'eil ect further raising of thebucket, because of the iact that the cir of said drums, and means automatically operated in dependence on the occurrence of a predetermined-phase ditlerenceof said drumsfor limiting the extentofthe independent controlling means for each of said motors/,

bucket a closing drum and a closing line connected .thereto for governing the closing f operation of said motors in both directions of rotation to prevent formation of slack in said cables. i

4. In a bucket hoist, a holding drum and a holding line connected thereto for governing the raising and the lowering of the andthe opening of the bucket, a separate independently operable electric motor for each of said drums, and controlling means for each of said motors including limit switch mechanism having cooperating parts which are connected to the respective drums to have relative movement in response to relative movement of the drums for limiting the eX- tent of the independent operation of said motors in both directions ofrotation to prevent formation of slack in said cables.

5. In a bucket hoist, a holding drum and a cable connected thereto for governing the holstlng and the lowering of the bucket, an

independently operable closing drum and a cable connected thereto for governing the opening and the closing of the bucket, a separateiindependently operable motor for each of said drums, independently operable starting and reversing controlling means for each of said motors, and electrical connections between said controlling means including limit switch mechanism having cooperating parts extent of the independent operation of said motors in either direction of rotation.

7. In a motor control, two'separately operable motors, independently operable controlling means for each of said motors whereby each motor may be operated in a forward or a reverse direction and means operable in response to the operation of one of said motors in either direction for limiting the independent operation thereof in. either direction ofrotation and for preventingthe operation of the other of said motors in a direction opposite to that of the first mentioned mot-or.

8. In a motor control, two separately oper able motors, separately operable elements connected tobe operated by said motors, independently operable starting and reversing controlling means. for each of said motors and connections between said controlling means including limit switch mechanism having cooperating parts connected to the respectlve elementsso' as to have relatlve movement in response to relative movement of said elements to thereby effect the automatic stopping of the motor being operated in either direction of rotationand the prevention of the starting of the other of said motors in the opposite direction While permitting the latterjmotor to start in the same direction of rotation as that of the first men tioned motor.

In Witness whereof, I have hereunto set my hand this 3d day of August, 1927.

LLEVELLYN C. IIAR'DESTY. 

